The present invention generally relates to methods and devices for interconnecting integrated circuit (IC) packages to printed circuit boards, e.g., in land grid array assemblies, using connecting devices having portions which are resilient or flexible.
In the mounting of an integrated circuit package to a printed circuit board (PCB), or similar support substrate, there are different methods of providing electrical interconnections between the package""s input/output (I/O) pads and the substrate""s pads. One method of interconnection, referred to as land grid array interconnection, uses a land grid array socket. This socket comprises a plurality of compressible conductive elements placed between the IC package and the substrate.
The compressible conductive elements are maintained in an array that corresponds to the package I/O pad array, by means of an electrically insulating matrix that acts as a contact support, or retainer. The land grid array socket is placed between the package and substrate. The IC package and substrate are held together with appropriate compression hardware, thereby causing each and every conductive element to be compressed and thus create appropriate contact force between its corresponding IC package pad and substrate pad, which ensures an electrically conductive path between those pads.
An example of a land grid array socket is shown in U.S. Pat. No. 4,922,376 to Pommer et al, entitled xe2x80x9cSpring Grid Array Interconnection for Active Microelectronic Elementsxe2x80x9d and issued May 1, 1990.
This patent describes the use of a plurality of conductive resilient elements, held in an insulating contact retainer having a plurality of apertures to hold each conductive element. The resilient elements provide an electrical connection between pads of the IC package and those of a substrate.
U.S. Pat. No. 5,139,427 to Boyd et al., entitled xe2x80x9cPlanar Array Connector and Flexible Contact Thereforxe2x80x9d, issued Aug. 18, 1992, shows another type of socket that can be used for land grid array interconnections. The individual contacts are formed of flat metal stock having spring characteristics including spring elements, held in a planar array by means of an insulating sheet fitted with openings, each opening containing a conductive spring contact.
In U.S. Pat. No. 5,273,438 to Bradley et al., entitled xe2x80x9cCanted Coil Spring Array and Method for Producing the Samexe2x80x9d, issued Dec. 28, 1993, electrical contact in the land grid array socket is provided by an array of canted coil springs.
U.S. Pat. No. 5,033,970 to Buchoff, entitled xe2x80x9cSelf-mounted Chip Carrierxe2x80x9d and issued Jul. 23, 1991, shows an elastomeric ring that provides electrical conductive paths, instead of individual elements as in the other documents cited above.
U.S. Pat. No. 5,832,601 to Eldridge et al., entitled xe2x80x9cMethod of Making Temporary Connections Between Electronic Componentsxe2x80x9d, issued Nov. 10, 1998, describes a method of attaching wires onto semiconductor dies, and use of these wires as resilient contact structures to perform electrical testing of the dies. This patent describes a method of manufacturing resilient contact structures, with soft core wires attached to a tip made from a sacrificial substrate, and subsequently coated with a hard material.
IC packages used for land grid array interconnection are usually ceramic or plastic type packages and, according to the present state of the art, as described above, have no interconnection means permanently attached to the metallized conductive I/O pads thereof
Another commonly used method for electrically connecting integrated circuit packages to substrates is known as surface mounting. For this type of connection, leads, solder balls, or any other solderable interconnection means are permanently attached to the IC package; which in turn are permanently attached to the printed circuit board pads by means of soldering. U.S. Pat. No. 4,751,199 to Phy, entitled xe2x80x9cProcess for Forming a Compliant Lead Frame for Array-type Semiconductor Packagesxe2x80x9d, issued Jun. 14, 1998, shows one example of a surface mountable component, with discrete compliant conductive elements suitable for surface attachment to the printed circuit board by conventional surface mount assembly soldering.
Comparing the aforementioned methods, it is understood that land grid array interconnections consist typically of a non-permanent mechanical assembly between the package and substrate, the package being demountable. This important advantage (demountability) is not available in the case of known surface mount assemblies. Furthermore, land grid array offers a more compliant interconnection than surface mount assembly, thereby offering improved reliability when such packages are submitted to thermal and mechanical stresses. On the other hand, land grid array interconnection methods typically require the use of a land grid array socket, which adds significant costs to the assembly. Use of a socket also requires precise alignment between the socket conductive elements and the package I/O pads, in order to provide the required conductive path to the substrate pads. Surface mount interconnection requires no such socket, since surface mount leads are already attached to the package before it is assembled to the printed circuit board.
Some work has been done by the assignee of the subject application in order to provide an electrical circuit package that could offer the combined advantages of surface mount and land grid array interconnection methods. For example, International Business Machines (IBM) Technical Disclosure Bulletin, September 1994, pages 395-396 entitled xe2x80x9cHigh Density Compliant Connector and socketxe2x80x9d, teaches the use of wire balls attached to an IC package, in order to provide a high density demountable interconnection.
It is one object of the present invention to provide an integrated circuit package which includes the combined advantages of surface mount and land grid array interconnections.
It is a further object of this invention to provide a new and practical connection device and method for interconnecting electronic circuit components.
It is another object of this invention to provide for connecting devices which can be readily connected to the I/O pads of an integrated circuit component.
It is still another object of the present invention to provide interconnections from one planar substrate to another, where the substrates can be selected from the group of printed circuit board, ceramic, or other substrate common in the field.
It is a further object of the invention to provide for a new interconnecting device and the use of such devices in integrated circuit packages and integrated circuit assemblies.
According to one aspect of the invention there is provided an electrically conducting device for interconnecting respective contact pads positioned on two separate components. The device is a homogeneous element and comprises a surface portion and a flexible portion. The surface portion is adapted to be joined to a contact pad on a first component and an end of said flexible portion is adapted to be pressed against a contact pad on a second component to thereby provide an electrical connection between said contact pads on the two components.
According to another aspect of the invention there is provided an integrated circuit package comprising a package having a plurality of I/O pads and a plurality of electrically conducting connecting devices each comprising a surface portion and a flexible portion. Each said surface portion is joined to an I/O pad on the package and an end of each of said flexible portions is adapted to be pressed against a contact pad of a component to thereby provide an electrical connection between an I/O pad on the package and the contact pad of the component.
According to yet another aspect of the disclosed invention there is provided an integrated circuit assembly comprising a first electrical component having a plurality of pads; a second electrical component having a plurality of pads; and a plurality of conducting devices each comprising a surface portion and a flexible portion. Each surface portion of a conducting device is joined to a contact pad of the first component, and an end of said flexible portion of each conducting device is pressed against a contact pad on the second component to thereby flex the flexible portion and provide an electrical connection between the contact pads of the two components.
According to a further aspect of the invention, there is provided a method of attaching conducting devices to an array of contacts on a first electrical component. Each device comprises a surface portion and a flexible portion with each surface portion adapted for being joined to a contact pad on a surface of a first component and an end of the flexible portion adapted for being pressed against a contact pad on a second component to flex the flexible portion and thereby provide an electrical connection between the contact pads on the two components. The method further comprises the steps of providing a fixture having openings corresponding to the array of contacts on the first component, loading a plurality of the conducting devices in the fixture to position the devices in the openings, positioning the fixture adjacent the first component, and thereafter attaching each conducting device to the corresponding contact of the first component.
Further details and advantages of the invention will be apparent from the following description of the preferred embodiments of the invention, illustrated in the accompanying drawings.